Shareholders' Equity - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	$ (566)	$ (545)
Other comprehensive income before reclassification	(5)	(7)
Amounts reclassified from accumulated other comprehensive loss	2	2
Net current-period other comprehensive income	(3)	(5)
Ending balance	(569)	(550)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(90)	(41)
Other comprehensive income before reclassification	(4)	(8)
Amounts reclassified from accumulated other comprehensive loss	0	0
Net current-period other comprehensive income	(4)	(8)
Ending balance	(94)	(49)
Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(476)	(500)
Other comprehensive income before reclassification	(1)	1
Amounts reclassified from accumulated other comprehensive loss	1	2
Net current-period other comprehensive income	0	3
Ending balance	(476)	(497)
Unrealized Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	0	(4)
Other comprehensive income before reclassification	0	0
Amounts reclassified from accumulated other comprehensive loss	1	0
Net current-period other comprehensive income	1	0
Ending balance	$ 1	$ (4)